1. Field of the Invention
The subject invention relates to engine sensor fault detection, and more particularly, to a method of detecting in-range sensor faults in helicopter gas turbine engines.
2. Background of the Related Art
Field experience with Full Authority Digital Electronic Control (FADEC) systems on helicopter gas turbine engines has shown that in-range, intermittent or slowly drifting sensor faults can remain undetected during conventional range and rate tests, when redundant engine sensors are not available for third party voting tests. In other words, in instances when only individual sensors are available, the intermittent or slowly drifting faults may not trip the rate threshold. Consequently, even though the engine control system may appear to be fully functional and capable for service at the time of launch, the dispatch capability of the helicopter may actually be limited.
It would be beneficial therefore, to provide a method of determining whether an in-range intermittent or slowly drifting sensor fault is indeed plausible in the absence of redundant, like sensors. With such a method in place, the loss of redundant, like sensors would not be critical to the safe operation of the engine and helicopter.
The subject invention is directed to a new and useful method of detecting in-range engine sensor faults in helicopters. More particularly, the method of the subject invention compares each of a plurality of engine sensors to all of the other sensors on the engine to determine whether any in-range, intermittent or slowly drifting sensor fault is indeed plausible. Thus, the loss of a redundant, like sensors would not be critical to the safe operation of the engine and helicopter.
The method of the subject invention includes the initial step of sampling input signals from a plurality of engine sensors, including sensors associated with the power turbine and main rotor speeds, high and low pressure spool speeds, compressor discharge pressure, turbine inlet gas temperature and fuel flow or burn rates. The method further includes the steps of computing the engine shaft horsepower for each engine sensor based upon the sampled input signal therefrom, computing a first mean horsepower from the plurality of engine sensors, computing the horsepower deviation from the first mean horsepower for each engine sensor, and computing a horsepower deviation ratio for each engine sensor relative to all of the other sampled engine sensors.
The method further includes the steps of disabling the engine sensor with the largest deviation from the first mean horsepower based upon the horsepower deviation ratio thereof, and computing a second mean horsepower after disabling the sensor with the largest deviation from the first mean horsepower. Thereafter, the horsepower deviation from the second mean horsepower is computed for each engine sensor, and the horsepower deviation ratio for each engine sensor relative to all other engine sensors is re-computed. The method further includes the steps of comparing the horsepower deviation ratios to predefined go/no-go limits, and declaring a sensor fault if the horsepower deviation ratio for an engine sensor exceeds a predefined limit.
Preferably, the step of computing engine shaft horsepower with respect to power turbine speed, main rotor speed, high pressure compressor discharge pressure and at least one fuel flow rate includes the step of conditioning the sampled power turbine speed signal, main rotor speed signal, high pressure compressor discharge pressure signal and the at least one fuel flow rate signal using respective first order lag filters.
Preferably, the step of computing engine shaft horsepower with respect to power turbine speed and main rotor speed includes multiplying the filtered power turbine speed signal and the filtered main rotor speed signal by the engine shaft torque signal, after the engine shaft torque signal has been conditioned by a first order lag filter.
Preferably, the step of computing engine shaft horsepower with respect to high pressure spool speed, low pressure spool speed and high pressure compressor discharge pressure includes applying respective engine performance maps to the high pressure spool speed signal, the low pressure spool speed signal and the high pressure compressor discharge pressure signal. Similarly, the step of computing engine shaft horsepower with respect to high pressure compressor discharge pressure and at least one fuel flow rate further includes applying respective engine performance maps to the conditioning high pressure compressor discharge pressure signal and the at least one fuel flow rate signal.
These and other aspects of the engine sensor fault detection methodology of the subject invention will become more readily apparent to those having ordinary skill in the art from the following detailed description of the invention taken in conjunction with the drawings described herein below.